ANALYTICAL CHEMISTRY
504 with a clean finger is always advisable just, prior t80placing the two surfaces together. Part 1 always should be placed on part' 2 with great care in order to avoid shock. It then should be moved gently in either direction and should slide smoothly. If not, a particle of grit may be suspected and the surfaces must be gone over again with a clean finger. Little difficulty has thus far been experienced in this laboratory in keeping the surfaces sufficiently clean. A surface, once in satisfactory operation, requires regrinding only after many runs.
If a particle of grit or steel does enter during the ruu, i t will immediately cause the machine t o leak. A circular score will be noted on both surfaces when t,he machine is taken apart. This is not a serious misfortune unless the score is very deep. Thtd difficulty often may he remedied as follow: A hole is cut in the center of a sheet of fine crocus cloth slightly larger than the diameter of the apparatus. This is placed between the sliding surfaces and the upper section gently revolved a few times. The cloth is then reversed, so that the abrasive is in contact with the other section. If this treatment does not stop t h r leakage, regrinding is advisable. Regrinding with fine emery requires approximately 2 hours. -1steel rod 0.25 inch in diameter and 18 inches in length is the only apparat,us required. The grinding compound is made by suspending t,he finest Turkish emery in Carbitol. The cent.ral rod, 3 of Figure 2, is removed together with the small circular plates which support 2. Section 1 is placed on a clean towel with the side to be ground facing upward. A limited amount of the grinding suspension is then spread rather evenly over the surface with a soft brush. Section 2 is placed gently on 1 with the surfare to be ground facing downward, and it is rotated gent'ly t o and fro in order to ensure a fairly even distribution of the emery. The steel rod is thrust through the central holes of section 2 but on11 through t8heupper hole of section 1 . The upper end of the steel rod is then grasped loosely and pushed in the plane of the surfaces as far as it will go without moving the lower section. The upper section, however, has been moved so that half or slightly more of the openings of tubes of t,he lower section have been uncovered on one side. By moving the upper end of the rod in a circular motion in the plane of the surfaces, a circular grinding action will be produced. The widest circle permitted by the rod and t,he hole in the lower section should be employed. K h e n the rod is held only loosely, i t will revolve in the hand and, furthermore, the upper sect,ion not only will move in a circular motion back and forth across the lower part but will also steadily progress from one tube to the next around the circle of t,ubes of the lower section. This is the effect desired. The motion should be smooth, never jerky. Fresh emery is added from time to time. At first. the film of emery is wiped clean from certain spots which become uncovered a t each stroke of the grinding action. These are the high spots. Later the upper section mill appear to slide more evenly on the loll-er and a uniform film of the emery will cover all t,he surface. The grinding operation is nearly finished at this point but the
grinding is continued somewhat longer. Upon washing, the deeper circular scores in the polished surfaces will still be visible, but these will not usually interfere. If leakage still persists a preliminary grind in which Carborundum is employed, may be required. When the number o f individual unit,s employed in mult,ipie ext,raction hecomes high, the mere washing of the tubes becomes a significant problem. From this standpoint the design of Figure I or 3 is extremely good, for here all the tubes are washed as H unit after a routine run.
In washing the larger apparatus of Figure 3, a large shallow pan which is not too wide to pass between the supports is placed under the apparatus. After the glass cover is removed, the upper sect,ion is turned midway from the position of coincidence of the tubes and sufficient distilled water or solvent to more than fill the lower section is poured in. When the solvent has flowed equally into all the tubes the upper section is lifted slight,ly. This permits the solvent to gush out through the sliding joint but will leave the lower section full. The upper section is again seated and the cover replaced. The tubes are tumbled a few times, then the glass cover is removed. The apparatus is carefully tilted so that, all the solvent will flow from the tubes and drop into the pan. Proper care should be taken during this operation that the upper section does not slide off the central stem aud that it is seated against the lower section before the whole is righted again. Several rinsings made as above may be required. However, the final rinse should he with acetone or alcohol. Ordinarily the lower glass plate is not taken off after a distribution, hut from time t o timr this is required for a more thorough cleaning. LITER 41'LrR E CITED
(1) Barry, G. T., Sato, Y.,and Craig, L. C . , J . B i d . Chrrn , 174, 209 (1948). (2) I h i d , ~ 1 7 4 221 , (1948). (3) Bush, M. T., and Densen, P. M., ANAL.CHEM.,20, 121 (19483. (4) Craig, L. C., J . B i d . Chem., 155,519 (1944). (5) Craig, L. C., Golurnhic, C.. Mighton, H., and Titus, E., Sciencr. 103, 587 (1946). (6) Craig, L. C., Hogebooni. G . H., Carpenter, F. H., and du Vigneaud, \',, J . Bid. Chem., 168, 665 (1947). (7) Craig, L. C., Mighton, H . , Titus, E., and Golumbir, C., bsar.. C H E Y . , 20, 134 (1948). (8) Gregory, J. D., and Craig, L. C . , J . B i d . Chem., 172, 839 (19481. \
-
~
~
~
I
Saal, 11. N. J., and Van Dvck. IT. J. D., First World Petroleum Congress, London, Proc., 2, 352 (1933). (10) Sato, Y., Barry, G. T.. and Craig:.L. C., J . B i d . Chem., 170, 501 (9)
(1947). (11) (12) (13) (14)
Stene, S.,Arkia. K e m i . .ViwruZ. Geol., 18A,Eo. 18 (1944). Tinker, J. F., and Brown, G . B., J . Bid. Chem., 173, 585 (19481. Titus, E. A . , and Fried. J.. [bid., 168, 393 (1947), 174, 57 (194x1. Williamson, B . , and Craig. L. C., I hid., 168, 687 (1947).
R E C E I V E DJ u n e 17, 1948.
PYCNOMETERS FOR OILS \I. R. LIPKIN, I. W. MILLS, C. C. RI..IRTIN, 4 N D W.T. H 4 K I E Y Sun Oil Company, ,%'orwood and Marcus Hook, Pa. Two designs of pkcnometers for the determination of densit! of oils art. dibrussed. The cup type is particularly suitable for density measurement a t a series of temperatures. The side-arm type which fills automatically by siphoning, is advantageous for w-ax) and extremely viscous stocks.
T(3,
HE; liteiature on density determination has been dircussed and a pycnometer described which is suitable for the de-
termination of density of 5-mI. samples of volatile liquids n i t h a n accuracy of 0.0001 gram per ml. This instrument could not be used for the accurate determination of density of viscour wmplw because of incomplete drainage in the capillaries. The density of viscous samples is frequently deterniined in apecific gravity bottles which are equipped with a plug having a capillary bore. Equipment catalogs usually list several modifications of this well-known type. K i t h thiq type of instrument,
error is introduced through difficulty in seating the plug 111 rxactly the same position for every determination. Trie aniount of sample remaining in the ground joint varies with the vi-cwity of the sample and the seating technique. Such errors arp niininiized by using large samples. The two designs of pycnometer presented in this paper ai? e~bhentially free from drainage error, and are satisfactory for the tietermination of density with a n accuracy of 0.0002 gram per nil. for \mall samples of viscous oils. Each pycnometer has partirular advantages which make it desirable in special application..
V O L U M E 21, NO. 4, A P R I L 1949
505
RADIUS 0.8CM
rinaed thoroughly with distilled hater, and dried in an oveii it[ about 100" C. At other times the pycnometer is cleaned with benzene, unless the sample is aqueous, when acetone is used foi preliminary rinsing. Commercial grade acetone is not used f o r final qashing, as it sometimes contains a nonvolatile residue Whenever wiping is necessary, a cloth wet with solvent i s u w i because wiping with a dry cloth produces static charge. CUP-TYPE PYCYOMETER
Design. T h e cup-type pycnometer, Figure 1, consists ot B (--shaped tube with a bulb blown in one arm and a total capacitj of 1, 3, or 5 ml. Both ends of the U-tube are of tubing 1 mm. in inside diameter with 5/12 standard-taper tips. Two cups of 0.8cin. radius and 0.4-cm. depth fit on these tips. The cups and bulb of a n individual instrument are permanently marked with the bame number to distinguish them from other instruments. ~ ~ ( ~ - s D M MO D MAX
I
' 0 N
i
-__l'hr cup-type pycnonwtc.r, Figure. 1, is particularly suit able for drnsity measurement at a series of temperatures. If it is desired t o make determinations at successively higher temperatures, it is necessary to fill the pycnometer only once, in contrast to many typrs that must be cleaned and filled after each determination. The sidearm pycnometer, Figurr 2, fills automatically by siphoning; this is advantageous for waxy and extremely viscous stocks, which must be charged at elrvated temperatures. This tiiitonititic charging method can be applied to either instrument. T h r determination of density involves measurement of the volume, of the sample a t a specified trst temperature, and measui'emerit of the weight of the sample. Precision densities of oils a r e usually determined a t 20" or 25' C. A glass jar thermostat with teinprrature controlled to *0.05' C. and an analytical bal: i i i ( ' e with a11 accuracy of 0.1 nig. are necessary. T o obtain weights a(-curate within 0.1 mg. it is necessary to avoid static on t hr. pycnometers and to correct for buoyancy effects. i~liargt~ Slatic: charge may be detected by attraction of the pycnometer for t tie wire hook in the balance. Such charges dissipate very slowly i t 1 a dry atmosphere, but can be eliminated by placing radioactive niaterials inside the balance case or increasing the humidity of the t)alance room-i.e., above 60y0 relative humidity. In this laboratory buoyancy corrections are not made for the Lvrighings in either calibration of the pycnometer or determination of density. The apparent volume of the pycnometer is obtained using distilled water. (The adjective "apparent" is used here to denote volumes or densities calculated without making tluoyancy corrections.) A single correction is finally a d d d t o the apparent drnsity, dA, of each sample:
C = 0.0012 ( I - d a ) (1) This oorrection is based on the use of an average value of 0.0012 gram per ml. for the density of air (4). Keights of the samtb clrnsity must be used in both the calibration and density detrrrninatioris. The conditions under which this correction may be used are thoroughly discussed in ( I ). Equation 29 of ( 1 )states thr cur,rection as d,,, (1 - dA/dwaterj. The claster a t 20" or 25" C. is sufficiently close t o 1 to have no significant effect on the correctinn; so this term is neglected in Equation 1. If an oil of known density is used for checking the water caliIration, it is necessary to subtract the above correction from the density in vacuum before calculating the apparent volume. Before calibration and whenever liquid fails to drain freely in t hi> c.apillaries, the pycnometer is (-leaned with hot chromir arid,
0 C 0.2 M M . 1.0.
NOTE -TOTAL WEIGHT NOT TO EXCEED 35 GRAMS
1 ' ~
ARRANGE HOOK SO THAT PYCNOMETER FILLED WITH WATER HANGS AT AN ANGLE
,,
2.0?0.5MM.I.D.
1
I Figure 2.
Side-Arm Type Pycnometer
Calibration. The apparent volume of the full pycnometer is determined in the following manner 8.t the test temperature, ririiip frtishly distilled water. T h e weight of the cleaned and dried pycnometer without cupq but with a 5-cm. (2-inch) length of clean dry rubber tubing, is determined to the nearest 0.1 mg. h xishbone-shaped hook is uscti to suspend the pycnometer on the balance. The pycnometer is inverted, the arm with bulb is placed i n a beaker of freshly distilled water, and gentle suction is applied nntil both arms are completely filled with ivater. The pycnometer is immediately righted, the cups are placed on the arms, and several drops of water are added to each cup. The assembly is then immersed in the thermostat to a point just below the bottom of the ground joints for 15 minutes. d suitable holder has beer described by Ledley (3). The cups are then removed, excess water is wiped from the tips by passing a finger lightly over each tip, and then the tips are carefully dried with a small piece of absorbent paper. I t is essential that the capillaries be completely filled a t this point. The rubber tubing previously weighed with the empty pycnometer is placed over the tips to take care of expansion and t o prevent evaporation. The pycnometer is removed from the thermostat, and the outside of the pycnometer is thoroughly cleaned and dried. S o solvent should come in contact with the rubber tubing. After the closed pycnometer and contents have reached balance case temperature they are weighed to the nearest 0.1 mg. The apparent volume of the pycnometer is determined from the weight of water in air divided by the density of water a t the test temperature, 0.99823 a t 20" C. and 0.99708 a t 25" C. The average of three determinations which agree within 0.0003 ml. is taken as the apparent volume of the pycnometer.
ANALYTICAL CHEMISTRY
SO6
"
apparent volume is calculated. Determination. The weight of the clean dry pycnometer with cups is determined t o the nearest 0.1 mg. The cups are removed and the pycnometer is inverted and filled with sample by gentle suction in such a way t h a t the sample contains no bubbles. For viscous samples the oil is heated before the filling operation. The pycnometer is immediately righted, the cups are placed on the arms, and a few drops of sample are placed in each sup. The assembly is then immersed in the thermostat for a t lea8t 15 minutes as described in the calibration section. The cups are removed, thoroughly cleaned, and dried. Excess sample is removed from the tins bv mssinn a finrer liahtlv over .. ~~
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_ ~~~
I
moved from'the bath', cleaned, and dried. ~ C m eshould be taken that no cleaning solvent gets into the cup joints. The pycnometer with cups is neighed and the density is calculatedas follows: d =
wt. of filled pycnometer - wt. of empty C pycnometer
+
apparent volume
~
~
(2)
Figure 4.
where C is buoyancy correction (Equation 1). SIDE-ARM TYPE PYCNOMETER
Design. T h e side-ann type pycnometer (Figure 2) is a Ushaped tube consisting ofashort armwith a W2standard-tapper tin and a lone arm with a. 0.25-ml. emansion bulb near the ton. Nkar the b o t b m of the l o w arm andther bulb is blown of suih
marked. -The side arm is not marked, as its weight dbes not enter into the determination. The rack used in filling this pycnometer by siphoning is shown in Figures 3 and 4.
&I
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9
IN OROOYE 8" SPRING
.*
I
. .. .. .........
F i g u r e 3.
Wooden R a c k Used in Filling Side-Arm Pycnometer
Calibration. The apparent volume of freshly distilled water is obtained near the top, middle, and bottom of the scales of the pycnometer. The volume is calculated by dividing the apparent weight of water by the density in vacuum a t the test temperature. A calibration curve is drawn, plotting the sum of the scale readings on both arms as the abscissa and the apparent volume in
~
Filling Side-Arm P y c n o m e t e r hy Siphoning
milliliters as the ordinate. All points must fall on the same straight line, which is the calibration curve for the pycnometer. A check calibration may he obtained using a pure hydrocarbon such as benzene. This calibration procedure is the same as used for the pycnometer for volatile liquids (S). If an oil of known density is available, a check oalihration point is obtained near the top of the SCRIP. Determination. OILSOF MEDIUMAND Low VI~COSITY.The pycnometer is weighed without the side arm to t,he nearest 0.1 mg. A 10-ml. sample beaker is placed on the wooden rack (Figure 3) and filled with bhe sample. Before the side arm is attached to the pycnometer a few drops of the sample are drained through to wet the inside surface, in order to avoid trapping air hubbles in the pycnometer during t,he filling operation. The side arm is placed on the pycnometer and the assembly is placed on the rack with the s/de arm dipping into the sample beaker (Figure 4). Gentle suction is applied to ihe long arm of the pycnometer until liquid 1s -pulled through the side arm into the graduated ann. The remsinder of the tilling is acoaniplished by siphoning. When the liquid reaches s a l e mark 6 on the long arm, the assembly 1s removed irom the rack placed in the thermostatcd bath, and held 1p the same tilted posikon until the oil ceases to contract. At thls point the short, arm should be full and the level in the long arm between 6.0 and 6.4. The sido a n n is removed, the tip is yiped off, and the pycnamet,er is placed in an upright positlan in the halder (S). The mater level in the bath should be above.scale mrLrk 5 and below the tip of the short mn. The final level In the shc~ntii~t~ly f 1 . c ~ . from alkali 1netal.j; rcrt~ntionof t h r of alkali meatal alkali nietal--1in the sintcwd mass; dr~pi~ndenct~ o n the. nature, partick size, and fu4l)ility of r l i ~hiimple: of niising the sample propcdy \\-it11 amiiioiiiuni c,hloridc arid c.alriuiii c a h o n a t r : and narrow tmiperaturc rangc necessary for. p r o p c ~~intt~ririy.Several niodifirations of t h r Smith procctdure havct I i w n dcscri1)ed. Stevens ( 1 2 ) proposed the us? ( i f I)ai,iuni c*hloridc. as a flux for sanip1t.s high in sulfate. Schole+ ( 1 0 ) sintered the saniplt, r i t h ralciuni carlwriatr and calriurn chloritlc~. SIakinrn (8) f u w t i tht. finely gronn(1 swmplc~ with ralciiirn rhlorirle alont~.
I n the Berzelius method (15) the pondered sample is decoriiposed by heating and evaporating with a mixture of sulfuric and hydrofluoric acids. Because of the ease of the initial decomposition of the sample by means of hydrofluoric acid, several modifications have been developed to simplify the subsequent steps in the procedure for recovering pure alkali metal salts. Iioenig ( 3 ) proposed the use of calcium oxide to precipitate elements of the R,O, group after the sample is decomposed with the acid niisture. Sullivan and Taylor ( 1 4 ) disintegrated glass samples with hydrofluoric and oxalic acids. Smith and Corbin (11) modified the niethod of Sullivan and Taylor, adding the successive use of 8-hydroxyquinoline (8-quinolinol) t o remove various elements. Schaal (9) described the elimination of many of the undesirable features of the original Berzelius method. Willard, Liggett, and Diehl ( 1 6 ) described the decomposition of silicates with hydrofluoric and perchloric acids, followed by fluoride removal, dehydration of residual silica, and separation of the potassium as the perchlorate by extraction of the soluble perchlorates with ethyl acetate. After the completion of the experimental u-ork described, Stevens (13) called t o the attention of the authors the
